Funds are requested to study the immunogenicity of Plasmodium berghei (rodent malarial parasites) cultivated in vitro. Although culture methods to date are not supportive of parasite invasion at frequencies permitting continuous culture, data from the applicant's laboratory indicate that intracellular parasite development proceeds normally to schizogony and merozoite release. Studies are planned to define the time course of development of functionally protective antigens on the parasite as development proceeds in vitro, after defining the minimum antigenic dose necessary to protect mice after challenge with the virulent NYU-2 line of P. berghei. Included will be studies of the possible inhibitory role played by non-merozoite antigens in causing a state of immune enhancement or specific immunosuppression. Polyacrilamide gel electrophoresis will be employed to monitor the quantitative and qualitative changes in parasite protein as development progresses, and to correlate these changes with the acquisition of functionally protective antigens by the parasite.